In the field of graphic arts, an image forming system that shows ultrahigh contrast photographic characteristics (especially with a gamma value of 10 or more) is necessary for improved reproduction of continuous dot image gradation or reproduction of a line image.
For this purpose, a special developer called a "lith developer" has heretofore been employed. This lith (lithographic) developer contains only a hydroquinone compound as the developing agent and a sulfite as the preservative. However, in order to prevent inhibition of the infectious developability of the hydroquinone compound, the sulfite has been used in the form of a formaldehyde adduct so as to keep the free sulfite ion concentration as low as possible (usually 0.1 mol/liter or less). As a consequence, the lith developer has a serious drawback in that it undergoes aerial oxidation so rapidly that its storage life is as short as three days.
For achieving a high contrast photographic characteristic with a stable developer, the use of various hydrazine derivatives has been proposed. Such hydrazine derivatives have been described in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606, 4,211,857, 4,243,739 and so on. By means of the use of such hydrazine compounds, satisfactory photographic characteristics such as ultrahigh contrast and high sensitivity may be obtained, and also the sulfite may be used in a higher concentration so that the stability of the developer against aerial oxidation may be increased over the conventional lith developer. However, such an image forming system is disadvantageous in that it gives rise to black spots which provide a serious problem to the photographic printing plate making process. These black spots, also known as black peppers, are tiny black specks appeared in the area between dots that is not intended to be developed and tend to increase and grow on aging of the photographic material and particularly during storage thereof under high temperature, high humidity conditions, or as the concentration of the sulfite ion used commonly as a preservative in the developer decreases or as the pH value of the solution increases. The formation of black peppers detracts considerably from the marketability of the product as a photographic material for manufacturing a photographic printing plate. Many efforts have been made to overcome this black pepper problem but improvement in black pepper is often accompanied by decreases in sensitivity and gamma, and there has been a strong demand for a photographic system conducive to an improvement in black pepper which does not entail losses of sensitivity and high contrast.